An example of a liquid conductor-based switch device is disclosed by Jonathan Simon et al. in A Liquid-Filled Microrelay with a Moving Mercury Drop, 6 IEEE J. OF MICROELECTROMECHANICAL SYSTEMS, 208-216. The disclosed switch device has a pair of cavities that are adjacent each other and connected by a communicating portion. Non-conductive liquid material is tapped inside the cavities. A drop of mercury is located in the communicating portion. A pair of terminals, which are disposed opposite each other, is also provided at the communicating portion. The mercury drop forms an electrical path in conjunction with the terminals.
A heater is provided in each of the pair of cavities. The heater can be turned on to heat the inside of one of the cavities and vaporize the non-conductive liquid material. The vapor forms a bubble inside the cavity. The heating raises the pressure inside the cavity, causing the non-conductive liquid material to push the mercury drop toward the other cavity. As a result of the movement of the mercury drop, an electrical path that is normally in a connected or xe2x80x9conxe2x80x9d state is put into a disconnected or xe2x80x9coffxe2x80x9d state. Conversely, movement of the mercury drop can put an electrical path that is normally in a disconnected state into a connected state.
In this switch design, the non-conductive liquid material cannot be kept in a stable state that is suitable for operation. For example, operation can become unstable when a bubble is unexpectedly generated, such as by a non-uniform change in temperature, and the vapor that makes up the bubble moves undesirably between the cavities. Also, the disclosed switch device does not switch smoothly between the connected and disconnected states.
In one aspect of the invention, a switch device comprises first and second cavities, a passage extending between the first and second cavities, a conductive liquid located in the passage and movable in the passage, an actuating liquid enclosed in each of the first and second cavities and covering inner surfaces of the first and second cavities, the actuating liquid being either an insulator or having low conductivity, and an actuating gas enclosed in each of the first and second cavities and existing as a bubble in each of the first and second cavities, the actuating gas being either an insulator or having low conductivity. In response to heating of the first cavity, part of the actuating liquid in the first cavity vaporizes and the actuating gas bubble in the first cavity expands, which causes part of the actuating liquid to be expelled out of the first cavity and the conductive liquid to move in the passage such that an electrical path that includes the conductive liquid changes from one of a connected and a disconnected state to the other of a connected state and a disconnected state. The first cavity includes a constriction element shaped to constrain the expansion of the actuating gas bubble in the first cavity.
In another aspect of the invention, a method for switching an electrical path in a switch device having first and second cavities, the first cavity including a constriction element, a passage extending between the first and second cavities, a conductive liquid located in the passage and movable in the passage, an actuating liquid enclosed in each of the first and second cavities and covering inner surfaces of the first and second cavities, the actuating liquid being either an insulator or having low conductivity, an actuating gas enclosed in each of the first and second cavities and existing as a bubble in each of the first and second cavities, the actuating gas being either an insulator or having low conductivity. The method includes vaporizing part of the actuating liquid in the first cavity and expanding the actuating gas bubble in the first cavity in response to heating of the first cavity. The expansion of the gas bubble in the first cavity is constrained by the shape of the constriction element. Part of the actuating liquid is expelled from the first cavity in response to the expansion of the actuating gas bubble in the first cavity. The conductive liquid moves in response to the expulsion of part of the actuating liquid from the first cavity, which puts an electrical path that includes the conductive liquid from one of a connected and a disconnected state to the other of a connected state and a disconnected state.